1. Field of the Invention
The present invention relates to a photosensor array for use in retrieval of a light signal in a photoelectric conversion device which is used as a read-out section of an image information processing apparatus.
2. Description of the Prior Art
Conventionally, a linear photodiode type elongated photosensor array made of silicon monocrystal has been used in a photoelectric conversion device which is used as a read-out section of an image processing apparatus, such as facsimile, and digital copier. The photosensor array of this type, however, has been restricted in its length in view of the available dimensions and precisions with which silicon monocrystals can be manufactured. For this reason, in the case of a wide original to be read out, an original image has been focused as a scaled-down image onto a photosensor array using an appropriate optical system. However, the introduction of such a scaling-down optical system results in a disadvantage in miniaturizing the read-out section.
Apart from the above, by virtue of development of film forming methods, such as glow discharge method, sputtering method, ion plating method, and vaccum evaporation method, or a method for coating a mixture of binding resin and semiconductor material, an elongated and large dimension photosensor array has been realized by using such technology.
A planar type photoconductive photosensor may be given as one example of photosensors constituting such an elongated line sensor, in which a pair of metal electrodes are formed on a photoconductive layer, such as amorphous silicon, chalcogenide, CdSor, CdS-Se, the pair of metal electrodes being disposed on the photoconductive layer facing each other so as to form a gap serving as a photoelectric conversion portion.
FIG. 1 is a brief partial plan view showing one example of such planar type photosensor arrays, and FIG. 2 is a cross sectional view along a line II--II of FIG. 1. In the figures, numeral 1 represents a substrate, numeral 2 is an amorphous silicon photoconductive layer mounted on the substrate, numeral 3 represents a common electrode, and numeral 4 represents a separate electrode. A gap portion at which each separate electrode 4 faces the common electrode 3 is a photoelectric conversion portion (i.e., pixel). In the figures, the pixels, are disposed in a 7.times.5(=35) array. The pixels are divided into seven blocks, each block including five pixels. The common electrodes 3 are respectively provided one for each block. The separate electrodes 4 are provided, at the opposite side of the photoelectric conversion portion, with an insulation layer 5. The insulation layer 5 is formed with a through hole 6 through which each separate electrode 4 of the block is connected to the corresponding one of five signal pick-up wires 7 mounted on the insulation layer 5. Therefore, the photosensor array can be driven in a matrix fashion by connecting to a driver circuit the seven terminals for the common electrodes 3 and five pick-up terminals for the pick-up wires 7.
Although the photosensor array with thirty-five pixels has been described with reference to FIGS. 1 and 2, in the case of an elongated photosensor array of a high density of pixels, the number of pixels may be 64.times.32=2048 for example. FIG. 3 shows an equivalent circuit diagram of such a photosensor array. In FIG. 3 C.sub.1 to C.sub.64 represent 64 common electrode terminals, I.sub.1 to I.sub.32 represent 32 signal pick-up wire terminals for the separate electrodes, and R.sub.1 to R.sub.2048 represent 2048 photoelecrric conversion portions. With the photosensor array as above, it is possible to derive outputs by sequentially applying voltages to the common electrode terminals C.sub.1 to C.sub.64 and sequentially driving the signal pick-up wire terminals I.sub.1 to I.sub.32 for the separate electrodes. The terminals C.sub.1 to C.sub.64 and I.sub.1 to I.sub.32 of the photosensor array are connected to a driver circuit. In this case, according to the conventional photosensor array, the terminal arrangement similar to that shown in FIG. 1 has been adopted heretofore. That is, as shown in the brief plan view of FIG. 4, the terminals C.sub.1 to C.sub.64 and I.sub.1 to I.sub.32 have been disposed along the marginal portion of the substrate in the direction of the array disposal in the photosensor array.
With the photosensor array constructed as above, it is required to make the pitch of mutual arrangement particularly of the common electrode terminals C.sub.1 to C.sub.64. The reason is that if a large pitch of arrangement is used, the area for wiring the common terminals 3 on the substrate 1 becomes very large and it is not possible to realize a compact photosensor array. In addition, generally the connections of the driver circuit to the terminals C.sub.1 to C.sub.64 and I.sub.1 to I.sub.32 are attained using a flexible wiring board so that if the terminal pitch is made too narrow, the connection work becomes hard to carry out. Thus, disadvantages arise such as the increase of the number of processes required in manufacture, and a lower yield.